Estrogen receptor α mediates the nongenomic activation of endothelial nitric oxide synthase by estrogen

Estrogen is an important vasoprotective molecule that causes the rapid dilation of blood vessels by activating endothelial nitric oxide synthase (eNOS) through an unknown mechanism. In studies of intact ovine endothelial cells, 17 beta-estradiol (E-2) caused acute (five-minute) activation of eNOS that was unaffected by actinomycin D but was fully inhibited by concomitant acute treatment with specific estrogen receptor (ER) antagonists. Overexpression of the known transcription factor ER alpha led to marked enhancement of the acute response to E-2, and this was blocked by ER antagonists, was specific to E-2, and required the ER alpha hormone-binding domain. In addition, the acute response of eNOS to E-2 was reconstituted in COS-7 cells cotransfected with wild-type ER alpha and eNOS, but not by transfection with eNOS alone. Furthermore, the inhibition of tyrosine kinases or mitogen-activated protein (MAP) kinase kinase prevented the activation of eNOS by E-2, and E-2 caused rapid ER-dependent activation of MAP kinase. These findings demonstrate that the short-term effects of estrogen central to cardiovascular physiology are mediated by ER alpha functioning in a novel, nongenomic manner to activate eNOS via MAP kinase-dependent mechanisms.